CRF Blog

How a Dubious Forensic Science Spread Like a Virus

by Bill Hayes

As part of its ongoing series titled Blood Will Tell: Investigating the Science Behind Forensic Science, ProPublica looks at How a Dubious Forensic Science Spread Like a Virus.

The prosecution’s star witness — a forensics specialist named Herbert MacDonell — set out an array of props before the jury: a medicine dropper, a mirror hastily yanked from the wall of the courthouse bathroom and a vial of his own blood, drawn that day at a nearby hospital.

It was a strange sight in the 1985 Texas courtroom, and the jurors, the judge and even the defense attorneys watched, rapt, as MacDonell laid the mirror flat and then climbed up on a chair, holding the vial and dropper.

MacDonell’s expertise lay in an obscure discipline known as bloodstain-pattern analysis. He claimed he could reconstruct the events of a crime by reading the bloodstains left behind.

Like a professor performing a classroom demonstration, he dipped the dropper’s tip into the blood and, with a practiced hand, released a single drop onto the mirror. It landed with a muted thud, forming a perfect crimson circle.

Blood landing on a flat surface should not spatter, MacDonell told the jurors with satisfaction. He let another drop fall onto the white shirt he was wearing. Blood lands differently on fabric, he showed them.

A defense attorney shot up from his chair in protest. This was a murder trial. There was no mirror at the crime scene. No medicine dropper. The demonstration was not reliable science, he argued. The judge disagreed.

MacDonell’s testimony would be pivotal to proving the Fort Bend County prosecutor’s theory that 21-year-old Reginald Lewis had murdered his family, shooting his mother and two brothers, and setting his father on fire. MacDonell had identified dozens of minuscule blood spots on Lewis’ clothing, and he said they placed Lewis at the scene during the crime

The jurors gave Lewis four 99-year sentences.

“MacDonell kind of took over the courtroom,” Lewis’ attorney, Donald Bankston, recalled, his disbelief still fresh. “It was almost like having Mr. Wizard.”

But MacDonell’s testimony that day did more than mesmerize the jury. It gave bloodstain-pattern analysis its first toehold of legitimacy in Texas courts, spreading it quietly, but surely, further into the justice system.

Two years later, Texas’ 1st Court of Appeals ordered a retrial because of evidentiary flaws (two retrials ended in hung juries), but it expressly rejected Lewis’ argument that bloodstain-pattern analysis was a “novel technique” that should never have been admitted and was not “scientifically recognized” or reliable.

“MacDonell’s studies are based on general principles of physics, chemistry, biology, and mathematics, and his methods use tools as widely recognized as the microscope; his techniques are neither untested nor unreliable,” Judge James F. Warren wrote for the court. To support his decision, Warren cited four other states — Tennessee, California, Illinois and Maine — that had already affirmed bloodstain-pattern analysis’ use at trial. Two of those states had based their decisions on court testimony by MacDonell. [more]